1. Field of the Invention
The invention relates to thermal viewers or detection devices which operate in the far infrared at a wavelength region around 5 microns and longer.
2. Description of the Prior Art
Current detection devices operating in the far infrared are total radiation detectors which do not discriminate between the frequencies in their band of operation. A step in this direction is described in patent application Ser. No. 130,957, filed Mar. 17, 1980, by Robert E. Callender, et al, now U.S. Pat No. 4,280,050 and having the same assignee as the present application. In this application, a thermal viewer is converted to a radiometer by placing a continuously variable filter in front of the detector and continuously monitoring the output sum of all detector channels. The output is recorded and may be analyzed by persons skilled in the use of this type of information. There is a need, however, for a radiometric device in this spectral region to discriminate between chemical agents present in the atmosphere, which supplies a general go-no-go type information which is easily interpreted by operators who are not skilled in spectral analysis.